Platinum plating process

ABSTRACT

The commutator segments of a rotatably supported assembled armature are shorted to the negative side of a DC voltage source and a platinum anode connected to the positive side of the voltage source is wet with an aqueous solution of chloroplatinic acid and an alkali metal compound such as sodium carbonate, the anode wet with solution being wiped across the shorted segments until a platinum layer builds up over the surface thereof. The proportions of chloroplatinic acid and sodium carbonate in the solution are such that platinum build up other than on the commutator segments remains sparse and isolated by the carbonate residue so that there is no shorting of the segments across the insulators.

[ Feb. 11, 1975 OTHER PUBLICATIONS Modern Electroplating, Fred Lowenheim, 2nd Edition,

ABSTRACT The commutator segments of a rotatably supported Primary Examiner-T. M. Tufariello Attorney, Agent, or Firm-Johnson, Dienner, Emrich & Wagner assembled armature are shorted to the negative side of a DC voltage source and a platinum anode connected to the positive side of the voltage source is wet with an aqueous solution of chloroplatinic acid and an alkali metal compound such as sodium carbonate, the anode wet with solution being wiped across the shorted seg- United States Patent Suggs PLATINUM PLATING PROCESS [76] Inventor:

221 Filed:

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. l u m sem mw t to ,9 nrmm.mtm :w mmu m mtdbmtS a m 7 Human a 222 4 222 2 O ///2/ S 2 OOO O n 222 2 O u ...H, I mmmmm T m mmmmm A m WNW: C m I mmmmm .L m nun P mmmmm P n ""n" A .m mm mm a uu muu R I, Mt.HS O B e ma s m mwhmw T m. HDnmLR W G 6773 A 7 46667 P 8 99999 8 HUM N 1 67608 G l I E 010579 R 4 2 5 58 0 0o v- F. 2, 4 8 4 PLATINUM PLATING PROCESS This invention relates to platinum finishing commutators and more particularly to a novel method or process and composition for platinum finishing the brush contacting surface of the commutator segments of an assembled armature. However, the invention also may be utilized to benefit slipring motor collector rings, DC. motor commutators, and universal type and repulsion-induction type commutators, as well as commutators used to transmit thermocouple temperature measurement signals.

Although such commutators are commonly constructed of copper, it long has been known that thelife of the commutators could be considerably increased by platinum finishing their brush contacting surfaces. With properly seated brushes, of the correct hardness, and operating under normal brush tension, a platinum finished commutator may be expected to have a life equal to several times that of copper and therefore last as long as the armature winding itself. Brush life is also extended in proportion to the decreasein friction between the brushes and the platinum finish.

Carbon, carbon alloy and graphite alloy of which the commutator brushes are commonly constructed attack both copper and platinum. Copper, however, is attacked more rapidly than is platinum because of its softness, ductility and greater physical surface resistance (friction). Shortly after a platinum finished commutator is put into service, a thin' carbon-platinum film builds up on its surface which serves to inhibit further attack of the platinum by the carbon brush. This film also reduces friction or resistance between the carbon brush and the high speedrotating contact surfacesof the commutator.

Platinum is thought of as having a relative electrical conductivity considerably less' than that of copper. However, because of its exceptional hardness, platinum, when applied in coats as thin as 0.0004 inches, is able to provide adequate protection in terms of wear resistance to the copper beneath. At that thinness of the platinum, the currentcarrying capacity of the copper beneath is not appreciably impaired; and the electrical conductivity of the platinum-coated copper approximates that of the copper alone.

Because platinum is a poor'thermal conductor at near room temperature (0.69 as compared to 3.91 for copper) the platinum film acts as a heat shield orblock for the copper and the carbon brushes actually decrease in resistance with a temperature rise. The electrical efficiency of the system will maintain proper thermal and electrical balance. The greater resistance of platinum to corrosion, its higher melting point (3,224

F as compared to l,98l F for copper) and its higher density (21.45 as compared to 8.96 forcopper) also contribute to the greatlyextended life of the commutator and brushes when platinum finished in accordance with the present invention. The platinum finish also provides resistance to spark erosion and high temperature. and by covering the copper segments it additionally prevents fragments of the copper from becoming embedded in the brushes and scoring the commutator surface. 7

In spite of all the advantages and features to be gained by platinum finishing the commutators, prior to the present invention platinum plating of the commutators has not been considered practical, commercially speaking. This has been true for a number of reasons. Included among these is the fact that commonly electroplating involves immersing or dipping the assembled commutator or its individual parts into a bath of electrolyte. This means that a substantial quantity of the electrolyte solution is required to conduct the plating process. Particularly where the commutator to be plated is of any substantial size, "the large amount of platinum required for the electrolyte solution has made the process prohibitively expensive. Also, when assembled with the armature, there is the problem of adequately preparing the armature to avoid deposition of platinum in areas other than the commutator slip rings or segments, for example on the armature windings and the insulators in the recesses between the commutator, segments or rings. This also increases the costs. Fur thermore, because in a dipping process the total com mutator is being plated at one time, considerable power is required. Depending on the size of the unit, to 1,000 amperes of current or more may be needed.

A principal object of the present invention therefore is to provide a practical and economical commercially acceptable means and method of platinum finishing commutators which will not be subject to the aforerecited and other. disadvantages.

In accordance with this invention, platinum finishing of the commutator may be advantageously delayed until after the armature has been finally assembled and the commutator need not be immersed in the plating solution. Instead the solution is applied to a limited number of the commutator segments by wetting an electrode with the plating solution and wiping the commutator segments therewith, the electrode being connected to the positive side of a voltage supply to which the electric segments being wiped are also shorted. Thus, depending on the size of commutator, one or more than one segment may be shorted to the negative side of the plating voltage which therefore may be kept very low, in the order of 10 or 12 volts.

Thus, a feature ofthe invention is that a process of platinum plating is provided which can be used to plate the commutators of very large as well as small armatures employing low voltage.

A further feature is that the costs of maintaining a large enough supply of the platinum electroplating solution is not necessary. In addition, there is a minimum waste in the practice of the invention.

A feature of the invention is that the electroplating solution with which the wiping electrode is wet contains only a small proportion of platinum ion producing compound such as platinic chlorideand the platinum plate is built up on the shorted segments by repeated wiping thereof with the wet anode. Because the proportion of platinum ion producing compound in the solution is so diluted in the solution, except on the shorted commutator segments, deposits of platinum is sparse, for example in the insulator receiving-slots between the commutator segments where some of the solution may unavoidably collect.

A further feature of the invention is that the electrolytic solution also contains sodium carbonate or other decomposable alkali metal compound which will maintain the solution alkalinity at a desired level during the plating process so as to hold the platinum compound suspended within the solution. At conclusion of the platingprocess as the water evaporates, the carbonate residue mixes with the platinum to avoid shorting of the commutator segments across the insulator containing slots. This carbonate residue also promotes ready clean I up of armature windings as by wiping with a damp cloth. Residue collecting in the insulator containing notches between the segments is also readily removed by passing the blade of a commutator notch knife through the slots.

Thus, important features of the invention include avoidance of the cost of maintaining a large supply of platinum solution since only a little more than the small amount of platinum consumed in the process is required to practice the electroplating process. At the same time the bother and expense of preparing the armature is avoided and a highly practical and economical process, commercially speaking, is provided for platinum finishing commutators and a process which may be practiced conveniently and by individuals of little skill, and upon the commutator after it has been finally assembled with the armature.

Many other objects, advantages and features of the invention will be at once apparent or will become so upon consideration of the specific description of preferred embodiments of the invention which follows.

Referring therefore to the single FIGURE which comprises the accompanying drawing, means are illustrated for mounting a completed armature having a commutator assembled therewith whose segments 22 are to be electroplated with platinum in accordance with the invention. As is conventional, commutator 20 comprises a plurality of circumferentially spaced copper segments 22 about the armature at one end which are electrically insulated from other components of the armature and from each other by strips ofinsulator material 24 in the slots or spaces 26 between the segments 22. In preparation for electroplating the exposed outer surfaces of segments 22 have been turned, undercut, polished and cleaned to be as free of even microscopic contaminants as possible. To facilitate application of the platinum to the surface of the commutator segments the armature 10 is rotatably supported by placing end portions of its shaft 12 in V-shaped cutouts 14 provided in the upper edge of the two spaced uprights of the illustrated support 16.

To eliminate a voltage drop through the armature winding 18 during the electroplating process, negative lead 30 of an adjustable DC voltage source 32 is directly connected to one or more commutator segments 22 as by clip 34 which connects to a bare wire 36 which has been tightly wrapped about the commutator segments 22 adjacent risers 28. As illustrated in the drawing, and particularly where the armature and therefore the diameter of its commutator is large, a weight 38 is suspended from bare wire 36 to assure a good electrical contact of the wire 36 with at least the uppermost one of the commutator segments designated 22a and on which electroplating is initially conducted. The positive side of the DC voltage source in turn is connected by positive lead 40 to a platinum electrode 42 encased by a sleeve 44 of suitable textile material which will absorb a quantity of electrolyte composition 46 when wet therewith from container 48. Electrode 42 is provided with an insulated handle 50 by means of which it may be conveniently manipulated.

In accordance with this invention the electroplating composition 46 comprises a dilute aqueous solution of a platinum ion producing compound such as chloroplatinlc acid H PtCl .H O which also contains a substan- EXAMPLE l Range chloroplatinic acid I part .8 to L2 parts sodium carbonate 25 parts 20 30 parts distilled water I00 parts I00 parts It is prepared by first completely dissolving the sodium carbonate into the parts of pure distilled water after which the chloroplatinic acid is added and dissolved into the solution. The ingredients and conduct of the dissolving steps should be at room temperature (68-85F). If not used immediately the composition also may be stored at said temperature.

The proportions of chloroplatinic acid and sodium carbonate may be varied within the limits as indicated and provide satisfactory results. However, increasing the indicated preferred ratio of 25 parts alkali metal carbonate to 1 part chloroplatinic acid in the solution also increases the alkalinity of the solution with resultant increased production of platinous oxide which is considered to be a contaminant to the electrolytic process. Conversely decreasing the preferred ratio of the decomposable alkali metal carbonate to chloroplatinic acid will interfere with the ionization of the chloroplatinic acid and thereby the platinum deposition. For most satisfactory results it is presently felt that the indicatedproportions of sodium carbonate and chloroplatinic acid should not be varied by much more than 15% in either direction. Also, to avoid deposition of platinum compound within the recesses 28 between the commutator segments 22 the concentration of platinic chloride in the water should not be substantially increased by more than 15%. Although the solution can be further diluted than indicated, the resultant drop in resistance and corresponding rise in current characterizing the solution will prolong the whole process unduly.

In place of sodium carbonate other decomposable alkali metal compounds which will maintain the required alkalinity (pH of 8 to II) of the chloroplatinic acid solution may be substituted. Examples thereof are sodium borate and potassium borate. Both of these compounds have characteristics similar to that of sodium carbonate. However, because of their heavier molecular weight proportionately larger amounts thereof will be required to suspend the chloroplatinic acid in the solution for proper electrolytic functioning. For example, in the above example I, it would take approximately 50 parts by weight of sodium borate or 30 parts of potassium borate to replace the 25 parts of sodium carbonate to hold the platinum in suspension. However, because of the resultant increased alkalinity of the solution the proportion of chloroplatinic acid will also have to be proportionately increased to avoid undue production of the black platinous oxide during electrolysis. Thus further examples of suitable electrolytic compositions in accordance with the invention are as follows:

EXAMPLE ll Preferred Range chloroplatinic acid 2 parts 1.7 2.3 parts potassium borate 50 parts 40 60 parts water 100 parts 100 parts EXAMPLE lll Preferred Range chloroplatinic acid 1.2 parts I 1.4 parts sodium borate 30 parts 25 35 parts water 100 parts I parts The electrolyte composition 46 having been prepared and a suitable quantity thereof added to container 48, armature 10 mounted as described with at least its uppermost commutator segment 22a shorted to the negative side of the power supply 32, with the power supply 32 turned on and set to deliver from 10 to l2 volts, the electroplating process is initiated by dipping electrode 42 of the anode applicator 54 into the composition 46 for a few seconds and long enough to obtain a good soaking of its sleeve 44 with the composition 46. The wet sleeve-encased electrode of the anode applicator 50 is then wiped to and fro across and also lengthwise of the shorted segment or segments 22a until a uniform gray luster appears on its surface which is indicative of platinum buildup. A small plastic pan 56 may be placed directly beneath the commutator 20 to catch any solution which drips therefrom and the caught solution is returned to container 48. Ordinarily platinum buildup will commence within fifteen seconds, depending on the size .ofthe area being wiped by the applicator 54 and current will rise from 5 to amperes. Once sleeve 44 of the applicator has become thoroughly soaked with the composition 46 and platinum deposition has occured, the voltage may be reduced to 7 to 9 volts for normal platinum build up. However, the voltage should not be permitted to fall below 6 volts since poor plating will result with piling up" of the plating material due to improper molecular bonding. The applicator should be kept in continuous motion and in one area until a platinum layer of about 0.0004 inches is deposited which is indicated by the appearance of the bright silvery grey platinum luster. A more uniform build up of the platinum layer will result ifa lengthwise or lateral movement of the applicator 54 is employed as opposed to a circular motion. Once a uniform luster is built up across the length and width of the shorted segment or segments being wiped, which may take from to 45 seconds, the armature 10may be rotated on its shaft 12 to short the next group of segments to the power supply 32. The wiping action is then repeated. The process is then continued around the commutator until all the segments of the commutator 22 have been wiped with the wetapplicator and all have developed the grey platinum luster. It will be understood that the applicator sleeve 44 is redipped periodically into the container 48 so as to keep the electrode sleeve wet with the electrolyte composition and the applicator is also kept in motion until the contrast of platinum appears against the copper segments 22 being wiped. At completion of the plating step, the commutatormay be wiped with a damp cloth or sponge to deactivate the chemical action and clean off any residue remaining on the segments and also to remove any residue that may have sloughed onto the armature winding or other adjacent areas of the armature. To

test the bond of the platinum plate, a piece of adhesive tape, etc., may be applied to the platinum, pulled quickly therefrom and checked to see whether any platinum clings thereto. 4

Due to the low concentration of platinum compound in the solution (1 part per parts water 25 parts sodium carbonate) platinum build up in the slots and between the commutator segments 22 is avoidednAny platinum compound present in the residue which re mains in the slots 28 between the commutator segments at the end of the electroplating will be sufficiently sparse and also distributed through the much larger amount of carbonate residue. Therefore, shorting between the commutator segments due to bridging of the platinum deposits across the slots is ordinarily not present, and at best minimal. However, to guard against any such possibility, the armature should be put on an external growler and tested for shorts and grounds. For appearance sake, and in the event the growler test does show a short, residue in the slots 28 can be readily removed by passing the blade of a com' mutator slot knife (not shown) 'therethrough. If the electroplating has proceeded properly as described above, after damp and dry cleaning and polishing, the surface of the commutator segments 22 will reveal a bright platinum shade of grey similar to the pure platinum of electrode 42.

It willbe further understood that instead of moving the anode applicator relative to the shorted segment or group of segments, it is also possible to hold the anode applicator 54 stationary and rotate the armature on its shaft. In this alternative method of practicing the invention means will be provided to maintain sleeve 44 about the platinum electrode 42 of the anode applicator 54 continuously wet with the electrolytic solution 46 and means will also be utilized to short each segment or segments of the commutator as it is rotated into contact with the anode applicator 54 to the positive side of the voltage supply 28.

From the above description of preferred methods and compositions for practicing the invention, it will, be apparent that all of the recited objects and features of the invention have been demonstrated as achievable in an entirely practical, convenient and economical manner. Furthermore, it will be appreciated that many other variations in the described process or composition may be utilized in the practice of the invention, the scope and bounds of which are defined by the appended claims.

Having described my invention, 1 claim:

1. A method of platinum finishing the insulationseparated commutator segments of an assembled arm ature which method may be conducted at room temperature, and utilizes a plating solution formed at room temperature by dissolving decomposable alkali metal acid salt and chloroplatinic acid in water, said method comprising the steps of successively shorting groups of the commutator segments of the armature to the negative Side of a low voltage supply, wetting an anode connected to the positive side of said voltage supply with the plating solution and wiping the shorted commutator segments with the wet anode. until a film of platinum builds up over the surface of the shorted commutator segments, the chloroplatinic acidbeing sufficiently diluted in the aqueous plating solution that platinum build up on the shorted segments proceeds only slowly and platinum onthe insulation between the commutator segments remains sparse, the proportion of decomposable alkali metal acid salt in the plating solution being sufficiently larger than the proportion of chloroplatinic acid therein to maintain an alkalinity level in the solution to hold the chloroplatinic acid'in suspension with minimal production of platinous oxide, and the decomposed acid salt of the dried residue of the plating solution which remains on the insulation between the platinum plated segments upon evaporation of the water intermixing with and isolating the platinum content of said residue so as to avoid shorting of the platinum plated commutator segments across the insulation therebetween.

2. A method as claimed in claim 1 wherein the deand 25 parts sodium carbonate per parts water.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION PATENT NO. 1 3,865,697 DATED F ruary 7, 1975 INVENTOR(S) Robert Suggs It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 6, (Claim 4, line 1) As shown:

4. The method of claim 1 Should be:

4. The method of claim 3 Signed and sealed this 6th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON r Commissioner of Patents Attesting Officer and Trademarks 

1. A METHOD OF PLATINUM FINISHING THE INSULATION-SEPARATED COMMUTATOR SEGMENTS OF AN ASSEMBLED ARMATURE WHICH METHOD MAY BE CONDUCTED AT ROOM TEMPERATURE, AND UTILIZES A PLATING SOLUTION FORMED AT ROOM TEMPERATURE BY DISSOLVING DECOMPOSABLE ALKALI METAL ACID SALT AND CHLOROPLATINIC ACID IN WATER, SAID METHOD COMPRISING THE STEPS OF SUCCESSIVELY SHORTING GROUPS OF THE COMMUTATOR SEGMENTS OF THE ARMATURE TO THE NEGATIVE SIDE OF A LOW VOLTAGE SUPPLY, WETTING AN ANODE CONNECTED TO THE POSITIVE SIDE OF SAID VOLTAGE SUPPLY WITH THE PLATING SOLUTION AND WIPING THE SHORTED COMMUTATOR SEGMENTS WITH THE WET ANODE UNTIL A FILM OF PLATINUM BUILDS UP OVER THE SURFACE OF THE SHORTED COMMUTATOR SEGMENTS, THE CHLOROPLATINIC ACID BEING SUFFICIENTLY DILUTED IN THE AQUEOUS PLATING SOLUTION THAT PLATINUM BUILD UP ON THE SHORTED SEGMENTS PROCEEDS ONLY SLOWLY AND PLATINUM ON THE INSULATION BETWEEN THE COMMUTATOR SEGMENTS REMAINS SPARSE, THE PROPORTION OF DECOMPOSABLE ALKALI METAL ACID SALT IN THE PLATING SOLUTION BEING SUFFICIENTLY LARGER THAN THE PROPORTION OF CHLOROPLATINIC ACID THEREIN TO MAINTAIN AN ALKALINITY LEVEL IN THE SOLUTION TO HOLD THE CHLOROPLATINIC ACID IN SUSPENSION WITH MINIMAL REPRODUCTION OF PLATINOUS OXIDE, AND THE DECOMPOSED ACID SALT OF THE DRIED RESIDUE OF THE PLATING SOLUTION WHICH REMAINS ON THE INSULATION BETWEEN THE PLATINUM PLATED SEGMENTS UPON EVAPORATION OF THE WATER INTERMIXING WITH AND ISOLATING THE PLATINUM CONTENT OF SAID RESIDUE SO AS TO AVOID SHORTING OF THE PLATINUM PLATED COMMUTATOR SEGMENTS ACROSS THE INSULATION THEREBETWEEN.
 2. A method as claimed in claim 1 wherein the decomposable alkali metal salt is a borate or carbonate of alkali metal.
 3. The method of claim 1 wherein the plating solution comprises about 1 part by weight of chloroplatinic acid per 100 parts of water.
 4. The method of claim 1 wherein the plating solution contains an amount of alkali metal carbonate in the order of 20 to 30 times its portion of chloroplatinic acid.
 5. The method of claim 1 wherein the plating solution comprises by weight about 1 part chloroplatinic acid and 25 parts sodium carbonate per 100 parts water. 